The present invention relates to a control device for vehicle speed which is adapted to automatically maintain a vehicle at the memorized vehicle speed, and more particularly to a control device for vehicle speed which is adapted to interrupt supply of power to an electronical control means for controlling the vehicle speed control device when it is not in use.
The control device for vehicle speed of this kind generally comprises a throttle driving means coupled to a throttle valve, a set switch means for memorizing a vehicle speed, a resume switch means for reading a vehicle speed, a vehicle speed detecting means, a vehicle speed memory, and an electronical control means which responses to actuation of the set switch means to store in the vehicle speed memory the value in accordance with an output signal from the vehicle speed detecting means at that time, which responses to the resume switch means to read out the content of the vehicle speed memory, and which controls the throttle driving means in accordance with the read-out content. When the set switch is held ON over a certain time during running of the vehicle, the running vehicle speed at that time is memorized and constant-speed control is started. Vehicle speed control is inhibited by a cancel signal from a brake switch or clutch switch, and actuation of the resume switch regenerates the memorized vehicle speed to effect constant-speed control again.
In the usual control device for vehicle speed of this kind, however, once a power switch is turned ON, power is always supplied to the electronical control device even if the driver has no intention of using the vehicle speed control device, so that useless power is consumed. In case the electronical control device comprises a microcomputer CPU, etc., the CPU executes the program at all times, so that the actual service life of the CPU is shortened. To avoid the above disadvantages, the driver himself may turn OFF the power switch of the vehicle speed control device when it is not in use. But such manual ON/OFF operation of the power switch is very troublesome.